The present invention relates to the making of hot beverages in general and, more particularly, to a method of and an apparatus for making coffee by using a continuous flow technique.
There are known various ways of making coffee which vary from country to country or from one geographical region to another in dependence on taste preferences of the population. Some of the most popular ways of making coffee in this country, if pouring hot water into a container containing a quantity of so-called instant coffee is disregarded, are a percolating technique, and a drip technique. When performing the percolating technique, hot water or steam is repeatedly passed through a quantity of ground coffee until it extracts the coffee flavor from the ground coffee. However, because of the numerous passes of the boiling water or steam through the same quantity of coffee, some undesirable taste ingredients may be extracted from the ground coffee as well so that the beverage has less than an optimum or desirable taste. Therefore, the drip technique is preferred by many people, since it extracts the coffee flavor but not the undesirable taste components.
In performance of the drip technique, water closely below its boiling temperature is passed through a quantity of ground coffee only once. However, as the water passes through the ground coffee quantity, it follows the path or paths of least resistance, that is, it flows through the largest interstices present in the coffee quantity, or forms such relatively large interstices as it flows through the coffee quantity. This means that certain areas of the quantity of ground coffee will be bypassed by the flow of the hot water, or will be exposed to only a small degree of extraction of the coffee flavor therefrom during the passage of the hot water through the coffee quantity. To avoid the possibility that this preferential flow of the hot water would result in too small an amount of the coffee flavor in the beverage, the suppliers of coffee pouches for the drip-type coffee machines include an excess quantity of coffee in their pouches, and the suppliers of cans of coffee for use in drip-type coffee machines recommend the use of an excessive amount of coffee by the consumer as well. This, of course, is very wasteful but unavoidable lest the flavor of the coffee beverage be compromised.
To remedy these deficiencies, it was proposed, for instance, in the U.S. Pat. No. 3,025,781, to confine a quantity of coffee in an annular space of a rotary member which rotates about a vertical axis onto which the annular space is centered at least during the introduction of hot or warm water into the annular space through a central inlet opening provided in a shaft on which the rotary member is mounted for joint rotation therewith. As the water emerges from the inlet opening, centrifugal forces attributable to the rotation of the rotary member and acting on the water during and after its emergence causes the water to flow in a path having at least a component in the radially outward direction, so that the hot water will flow through the quantity of ground coffee present in the annular space and extract aromatic substances and other solubles therefrom. Then, the thus obtained coffee extract or beverage flows out of the annular space through perforations or openings provided in the peripheral edge portion of the rotary member. In this arrangement, water flows through the quantity of coffee only once, on its way from the central inlet toward the peripheral perforations, without being returned, so that the danger of acquisition of undesirable taste by the beverage is avoided. Additionally, the centrifugal forces caused by the rotation of the rotary member will also act on the quantity of coffee present in the annular space of the rotary member, so that the ground coffee will be somewhat compacted and thus undesirably large interstices will be avoided.
However, experience with this type of equipment has shown that the dwell time of the water in the annular space, which is determinative of the amount of extracted aromatic and other soluble substances, is usually too short for completely extracting the requisite amount of the substances, be it because the rotating speed is too small to achieve the requisite reduction in the size of the interstices, or because the rotating speed is too high so that the centrifugal forces cause the water to penetrate through the ground coffee too rapidly, despite the aforementioned compaction of the ground coffee. Although the aforementioned compaction tends to prevent the large interstices from forming, some channeling and bypassing of the coffee grounds takes place, especially along the walls bounding the annular space of the rotary member. A coffee making apparatus operative to lessen the channeling and bypassing problem is described in pending U.S. application Ser. No. 439,376, filed Nov. 5, 1982, by Dan Ben-Shmuel, and entitled METHOD AND APPARATUS FOR MAKING COFFEE now abandoned.